Pubs
The Scots don't really seem to have a strong "pub culture" like the Irish do -- there are pubs aplenty, but they are more often restaurants, too, and the customary pint after work doesn't seem to be the norm, here.
Ordering at the bar
In most pubs, you order at the bar. There is no waiter service. The way to do this, I have been told, is to stand at the bar and wait to catch the bartenders eye -- he/she will nod to acnkowledge you. When they make eye contact, make a hopefully sort of face, and they will either ask you immediately or hold up a 'wait a mopment' gesture and will get to you as soon as you are 'next'. Don't push, don't wave, don't just bellow out what you want -- there IS a queue, and everyoen in the pub is aware of it, even if you aren't, so wait until you are 'called on' . The queue might be invisible, but they bartenders have a it all in their heads, I promise. Hold money or your glass in your hand so it's clear you are in line, and they will get to you.
If you are still waiting and no one seems to have noticed, you are allowed to be a bit more sutble -- rotate the glass, perch an elbow on the bar. Still, do not call out, do not wave, do not tap money on th bar, and don't raise your whole arm. Definitely mark of an amateur, there. The only people allowed to say anything are regulars. They are given leeway you will not be shown.
When you want a refill, the process is much she same - you can subtly gesture to the bartender (a raised finger or slightly raised glass) and they will get you another. I have no idea how the figure this out, to be honest, all I can think of is some sort of hive-mind that gets generated when everyone sits at the bar.
Buying for the table
Send one person up to the bar, not everyone. Bring two people if you need to carry a lot of glasses. If you order for the table, you wil lbe given the total for the whole group, if it was your intention to pay separately, then you need to order separately.
Pay in cash, when you order the drinks. You will rarely be able to have a tab, and using a credit card in a busy pub might get you shunned, or worse.
What to order
Men order whisky or beer, or you're likely to be seen as effeminate. Women often order half-pints or foofy drinks.
Order Guinness first
If you're ordering a bunch of drinks, call out the Guiness (or Beamish or Murphy's) first. They take a while to pour and need to 'settle' before they can be drunk. Don't get antzy about the wait, it's necessary. The glass will sit on the bar for the head to properly settle -- don't make the mistake of trying to snatch it too early!
The terminology for things is always a bit of a mystery, so it's better to mark yourself a tourist and order explicitly "I'll have a pint of Smithwiicks" or "a half-pint of Guiness, please" than try to figure out the weird code of "half of bitter", "a half" or "glass of lager".
Ordering Food
Many pubs have a 'snack' menu -- simple stuff like hamburgers, pizza, etc). Order these at the bar as well. They will usually be delivered to your table, but you're on your own for ordering most of the time.
Info from the experts
Kate Fox has a book -Passport to the Pub which outlines all of these details only a sociologist could love. It's fascinating!